Does Life on the Seafloor Predict Life on Other Worlds?

byAmy Shira TeitelonJanuary 10, 2012

White smokers near the Marianas Trench. Could similar features exist, and breed life, on other worlds? Image Credit: National Oceanic and Atmospheric Administration

Scientists have recently discovered communities of previously unknown species living on the seafloor near Antarctica clustered around hydrothermal vents. This discovery is certainly exciting for biologists, but it’s also important for astrobiologists. It begs the question — if life can thrive in the deep, dark oceans without sunlight, could similar life thrive elsewhere in our solar system or the universe?

For decades, scientists assumed the deep oceans were barren; sunlight can’t reach the ocean floor, making it an impossible environment for life as we know it to arise. But in 1977, oceanographers from the Scripps Institute discovered hydrothermal vents.

These fissures, found along mid-ocean ridges on the seafloor of the Pacific, Atlantic, and Indian Oceans, create a natural, deep-sea plumbing system. Heat and minerals from the Earth’s interior vents out, providing a complex ecosystem that can reach up to 382 degrees Celsius (almost 720 degrees Fahrenheit). These ecosystems can support unique life forms that get their energy not from the Sun but from breaking down chemicals issued from the vents such as hydrogen sulphide.

The latest life forms, discovered in the Antarctic region by teams from the University of Oxford, University of Southampton and British Antarctic Survey, include a new species of yeti crab, starfish, barnacles, sea anemones, and potentially an octopus.

“These findings are yet more evidence of the precious diversity to be found throughout the world’s oceans,” said Professor Rogers of Oxford University’s Department of Zoology. “Everywhere we look, whether it is in the sunlit coral reefs of tropical waters or these Antarctic vents shrouded in eternal darkness, we find unique ecosystems that we need to understand and protect.”

Jupiter's moon Europa. The lines on the surface are breaks in the ice that lie on top of vast oceans. Image credit: NASA/courtesy of nasaimages.org

But it isn’t only biologists studying life on Earth that can benefit from this latest discovery. These peculiar environments on and beneath the seafloor could be a model for the origin of life on Earth and on other planets.

One particular target is Jupiter’s moon Europa. Recent research has confirmed that the moon has vast oceans buried beneath its frozen surface ice; it’s estimated to hold twice as much water as Earth. As such, it is a target for NASA in the search for life. It could be the case that some type of hydrothermal vent system exists on Europa, making its distance from the Sun irrelevant for life.

But just because sulfur or methane-based life on Earth can thrive around deep-ocean vents doesn’t mean the same is true on Europa. The presence of hydrothermal vents depends on geologic activity and a hot interior, neither of which has been confirmed. The possibility remains that light energy from the Sun could travel the distance to the moon and provide shallower portions of the subsurface oceans with life-giving light.

In any case, as scientists discover life in the more extreme environments on Earth, analogies are drawn with other worlds. If life is discovered in hostile parts of our planet, the same could theoretically arise in similar environments on other worlds.

Amy Shira Teitel is an historian of spaceflight, blogger, and freelance writer. Her blog, Vintage Space , chronicles her love of space history and manned space exploration. She contributes to Universe Today and motherboard.tv.

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Unfortunately, every Antarctic “new” life form is simply an adaptation from an existing and already varied branch of sea life. The blood worms at least, were more like a complete new species. This indicates that life, begun in ease can manifest itself in areas not as conducive to thriving. It does not indicate that there might have been an alternate basis for life or that species may have grown separate to our known biological tree. IMHO, this does practically nothing for astrobiological likelihood. I am sure that in a giant underground (er…underice) ocean, that there are bound to be thermal anomalies similar to Earth’s. Undoubtedly, where there is heat, there are heat extremes.
What I’m saying is that life needs a chance to start…THEN it can wander about adapting and becoming specialized.

But you are making a assumption, based on limited facts. At the end of the day these environments are few and far between, life in them is at a disadvantage as more energy rich locations are plentiful on planet earth. Life that would fully rely on them would simply not be able to compete today unless it was in complete isolation and devolved from the life that we see now. But earth wasn’t always a sunny, temperate, oxygen rich paradise, some 3.5 billion years ago the tables were turned, oxygen sucking photosynthetic life would have been at a disadvantage. Its unfortunate that our understanding is so limited from those periods of time, we really dont know much. In anycase if life can evolve in one direction then it can evolve in the reverse based on conditions. At the end of the day I think it has been shown pretty well that stability of a environment is the most important thing, if the surface of earth was oxygen and sun deprived but was conductive to these “extreme” life forms I dont see how you could think that they would not thrive in their own relative way and evolve with the stability and size that we have in our environment. Now I guess the problem is if there is any other place in our solar system that is “energy” rich and stable, and by stable I mean stable for hundreds of millions of years, pretty stable for a billion plus years. It certainly doesnt seem like it, though Europa is probably the best candidate for a stable environment with the necessary energy sources that could allow life to thrive and evolve in a different environment then the 99.999999999% of life on earth.

As you can see from my own reply to Peristroika I have to agree with you too.

But I have a few nitpicks on the biology:

– The process is “evolution”, and it is a stochastic & deterministic causal process that can only proceed forward as adaptation or drift fixes genes. (I.e. see to it that certain alleles of a gene is in a stable proportion in a population.) Biologists never say “devolve” because it doesn’t make sense for this process of fixation.

Species can both gain (say, predators) and loose (say, parasites) traits. But they have to do so from what they start out with. Most of the time you find that alleles can’t be loosed to loose a trait due to what is called “interlocking complexity”.

It was an evolutionary prediction of Muller in the ~ 30’s and it has been confirmed recently on a molecular biology level by several experiments. The most famous is perhaps Lenski et al work:

“They also found that the ability to use citrate could spontaneously re-evolve in populations of genetically pure clones isolated from earlier time points in the population’s history. Such re-evolution of citrate utilization was never observed in clones isolated from before generation 20,000. Even in those clones that were able to re-evolve citrate utilization, the function showed a rate of occurrence on the order of once per trillion cells. The authors interpret these results as indicating that the evolution of citrate utilization in this one population depended on an earlier, perhaps non-adaptive “potentiating” mutation that had the effect of increasing the rate of mutation to citrate utilization to an accessible level (with the data they present further suggesting that citrate utilization required at least two mutations subsequent to this “potentiating” mutation). More generally the authors suggest that these results indicate (following the argument of Stephen Jay Gould) “that historical contingency can have a profound and lasting impact” on the course of evolution.[2]”

– Oxygen is produced by photosynthetizers. Only plants have to consume it too, cyanobacteria generally doesn’t.

– Oxygen is harmful for chemical evolution possibilities, it breaks down organic compounds efficiently and is a strong poison of many processes.* Most geochemists would be wary of having free oxygen in putative abiogenesis environments, I think.

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* As I mentioned here recently, of the oxidization (in the chemical sense of increasing oxidation potential) the biosphere is responsible for, it is claimed that ~ 75 % of it goes to making Fe3O4 out of plate tectonic FeO products, ~ 25 % goes to oxidizing sulfur compounds, and ~ 1-2 % goes to making free oxygen.

Abiogenesis can be seen as the process of making CH4 more efficiently out of primordial CO2 with the help of biological enzymes.

Conversely, photosyntesis of the modern biosphere is the process of making Fe3O4 more efficiently. In other words, life is the business of making more rust. (O.o)

I agree with the general sense here, this is more telling on adaptation of biological evolution. Early life was likely less robust because it wasn’t as diversified or individually capable. We know that the DNA UCA was about as complex as today’s prokaryotes from gene family estimates, but the RNA world couldn’t be as RNA had to be in the form of populations of many small strings instead of a prokaryote’s few DNA strings.

But generally these finds of modern complex communities or animals points to possibilities, see my ref to oxygen-free animals above. This is how biologists have been using them in a long tradition going back to Darwin and his peers.

When a differentiated body cools down, metabolic network chemical evolution is at its fastest. Hydrothermal vents would provide longer lasting refuges and more energetic redox energy sources for these networks as the body cools further.

In addition, the separation between reducing and oxidizing environments as well as the thermal cycling provides a more differentiated chemistry. As well as an initial compartmentalization into chemical cells that drives smaller compartments down to the size of vent pores.

A pore opening is enough to set up an electrochemical potential difference akin to what closed cells utilize, which is telling on how naturally these environments tend towards cellular systems.

Alkaline systems (on Earth supplemented by plate tectonics subduction zones) produces polyphosphates which is halfway to catalytic heaven: in the form of AMP/ATP it is a cofactor for nucleotide production.

Here is a possible pathway to an RNA world:
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Spontaneous ligation takes mononucleotides to polynucleotides of ~ 100 base pairs, and recombination with the help of the cool-heat and concomitant pH cycles takes such heterochains to ~ 200 or more base pairs.

This is today close to the range of selfreplicating genetic material, the record holder is less than ~ 200 base pairs and manage to replicate ~ 96 % of itself with good efficiency. Such a molecule needs spontaneously formed lipid membranes to isolate it from replicating intruding competitors and go through the phase transition to procreation.

The increased production of these catalytically capable systems by faithless cloning sets the stage for genetic takeover of the catalytic metabolic network by the biological means of variation and selection of traits.

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Such abilities of hydrothermal vents keep up to the scale of multicellulars. Something like eukaryotes are needed for complex multicellulars because they alone produce enough energy to support enough traits. We do that by our many copies of simplified efficient energy factories of mitochondria.

I used to think we needed oxygen, and hence unavoidably some photosynthesis, for that. Even our hydrothermal vent communities have access to that today, which enable them to wring more redox energy out of the nutrients the prokaryote primary producers make with or without oxygen.

“In other words: They’ve found the first animals living without oxygen.

They belong to the group called loriciferans, a phylum of creatures that live in marine sediment. About a millimeter long, they look something like a half-jellyfish, half-crab. The beasts live in conditions that would kill every other known animal. As well as lacking oxygen, the sediments are choked with salt and swamped with hydrogen sulphide gas […]

Unlike plants, all previously discovered animals, and fungi, the newly discovered animal species don’t use mitochondria, the cellular organelle that converts sugar and oxygen into water, CO2 and, energy, to power their cells [Popular Science]. Instead, the animals pack the hydrogenosome organelle, a feature common among the miccoorganisms that live in oxygen-free zones.”

The question is whether this can exist on Enceladus. Europa might be a better bet, but I doubt we are going to drill through the ice mantle at all soon. A fly through of the geyser jets flying off of Enceladus seems more technically feasible.

There are also cold seeps on Earth, which have low temperatures (though I couldn’t find exactly how low, but I’m guessing no lower than 2C), which could be a possibility for life on other worlds. I’m not sure if hydrocarbons could seep out on other worlds, like they do here.

Good to know! Certainly low temperatures promote nucleotide formation, to the degree that Miller and others have suggested ice-thaw cycles as the formative environment instead.* Cold seep circulation could be a variant, and come to think of it methane clathrates formed at high pressures a potential alternative to water ice for that matter.

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* I think the high temperature processes that kicks in earlier and is generally more productive will have the advantage in general.

Then again, the universes is large so these things will likely happen once on a blue ice moon too.

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Is anyone aware of research on the DNA ancestry of these life forms? It might be possible to determine if they evolved from related organisms from the surface or the other way around–or if any of them went on a separate path.